Split python string by predifned indices

Question

I have a string that I'd like to split in specific places into a list of strings. The split points are stored in a separate split list. For example:

test_string = "thequickbrownfoxjumpsoverthelazydog"
split_points = [0, 3, 8, 13, 16, 21, 25, 28, 32]

...should return:

>>> ['the', 'quick', 'brown', 'fox', 'jumps', 'over', 'the', 'lazy', 'dog']

So far I have this as the solution, but it looks incredibly convoluted for how simple the task is:

split_points.append(len(test_string))
print [test_string[start_token:end_token] for start_token, end_token in [(split_points[i], split_points[i+1]) for i in xrange(len(split_points)-1)]]

Any good string functions that do the job, or is this the easiest way?

Thanks in advance!

Python doesn't have `out-of-the-box` split at position feature, if you ask for built-in function — deathangel908, Jul 14 '17 at 14:03

randomir · Accepted Answer · 2017-07-14T14:24:33.867

Like this?

>>> map(lambda x: test_string[slice(*x)], zip(split_points, split_points[1:]+[None]))
['the', 'quick', 'brown', 'fox', 'jumps', 'over', 'the', 'lazy', 'dog']

We're ziping split_points with a shifted self, to create a list of all consecutive pairs of slice indexes, like [(0,3), (3,8), ...]. We need to add the last slice (32,None) manually, since zip terminates when the shortest sequence is exhausted.

Then we map over that list a simple lambda slicer. Note the slice(*x) which creates a slice object, e.g. slice(0, 3, None) which we can use to slice the sequence (string) with standard the item getter (__getslice__ in Python 2).

A little bit more Pythonic implementation could use a list comprehension instead of map+lambda:

>>> [test_string[i:j] for i,j in zip(split_points, split_points[1:] + [None])]
['the', 'quick', 'brown', 'fox', 'jumps', 'over', 'the', 'lazy', 'dog']

Why the lambda? You can unpack the tuple in a list comprehension and just do `[test_string[i:j] for i,j in zip(split_points, split_points[1:] + [None])]` — tobias_k, Jul 14 '17 at 14:04
You're right, when thinking "functional", I always astray to `map` and `lambda`. `:-)` — randomir, Jul 14 '17 at 14:09

score 2 · Answer 2 · answered Jul 14 '17 at 14:02

This may be less convoluted:

>> test_string = "thequickbrownfoxjumpsoverthelazydog"
>> split_points = [0, 3, 8, 13, 16, 21, 25, 28, 32]
>> split_points.append(len(test_string))
>> print([test_string[i: j] for i, j in zip(split_points, split_points[1:])])
['the', 'quick', 'brown', 'fox', 'jumps', 'over', 'the', 'lazy', 'dog']

score 0 · Answer 3 · answered Jul 14 '17 at 14:02

0

First draft:

for idx, i in enumerate(split_points):
    try:
        print(test_string[i:split_points[idx+1]])
    except IndexError:
        print(test_string[i:])

answered Jul 14 '17 at 14:02

kchomski

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Split python string by predifned indices

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